Novel methine dyes

ABSTRACT

The present invention relates to novel methine dyes, methods for the preparation thereof and use thereof for dyeing plastics, especially polyamides, so as to obtain yellow to orange colourings with improved light fastness and improved thermal stability.

The present invention relates to novel methine dyes, methods for the preparation thereof and use thereof for dyeing plastics.

BACKGROUND OF THE INVENTION

Although there are already numerous yellow dyes on the market for colouring plastics, demand still exists for novel dyes with improved properties. In particular, there is a demand for known dyes improved with respect to their fastness. This applies in particular in the case of the use for bulk colouration of polyamide.

The bulk colouration of synthetic polyamides presents higher requirements of the colourants used than the bulk colouration of other plastics. The processing temperatures of synthetic polyamides, particularly in combination with glass fibres, are considerably higher and also the chemical reactivity of molten polyamides, especially of nylon-6.6, is substantially higher such that the heat stability of the colourants used has to be exceptionally good. Pigments generally have high thermal stability. However, there are few pigments which satisfy the high requirements in the case of bulk colouration of plastics, particularly if high light resistance is also additionally required.

Pigments are known from the prior art which are suitable for colouring plastics in shades of yellow.

DE-A 3543512 A1 describes pigments based on azo lakes (Bayplast® yellow G) which may be used for colouring polyamide in shades of yellow.

EP-A 0074515 discloses pigments based on nickel azo barbituric acid complexes which may likewise be used to achieve yellow colouring of polyamide.

Furthermore, long known is the use of Pigment Yellow 192 (C.I. 507300) to achieve yellow colouration of plastic.

Although the pigments mentioned have good thermal stability, no transparent colouration of plastics can be achieved therewith. Pigments can also impair the mechanical properties of the polymers. The use of solvent dyes is known from the prior art in order to colour plastics in transparent shades of yellow. The mechanical properties of polymers are generally not adversely affected by dyes.

Known solvent yellow dyes are e.g. Solvent Yellow 114 (C.I. 47020) from the class of quinophthalone dyes, Solvent Yellow 160:1 (C.I. 55165) from the class of coumarin dyes and also Solvent Yellow 179 (N-2-((4-cyclohexyl)phenoxy)ethyl-N-ethyl-4-(2,2-dicyanoethenyl)-3-methylaniline) and Solvent Yellow 93 (C.I. 48160), both from the class of methine dyes.

The properties of these yellow colourants known from the prior art are not however always sufficient for current existing technical requirements and are in particular in need of improvement regarding their fastness properties, particularly their thermal stability.

Furthermore, yellow methine dyes having good light fastness are known from EP-A 3 048 138, which also represent an improvement with respect to their thermal stability compared to the prior art presented above, but are nevertheless worthy of further improvement since the performance requirements in terms of polyamide colouration have increased even further.

SUMMARY OF THE INVENTION

The present invention relates to novel methine dyes of the formula (I)

in which

-   R¹ is hydrogen, halogen, COOH or COOR¹¹, -   R² is hydrogen, halogen, COOH, COOR¹² or CN, -   R³ is alkyl or phenyl, -   R⁴ and R⁵ are each independently alkyl, -   R⁶, R⁷, R⁸, R⁹ and R¹⁹ are each independently hydrogen, halogen,     alkyl, alkoxy or COOR¹³, and -   R¹¹, R¹² and R¹³ are each independently alkyl.

DETAILED DESCRIPTION OF THE INVENTION

Alkyl in the definitions of R³ to R¹³ refer for example to straight-chain or branched C₁-C₆-alkyl, preferably straight-chain or branched C₁-C₄-alkyl, especially methyl, ethyl, n- and isopropyl and also n-, iso- and tert-butyl, which may in each case be optionally mono- or polysubstituted by the same or different substituents, for example by halogen, such as chlorine, bromine or fluorine, and also by —OH, —CN, —NH₂ or C₁-C₆-alkoxy.

Alkoxy in the definitions of R⁶ to R¹⁹ refers for example to straight-chain or branched C₁-C₆-alkoxy, preferably straight-chain or branched C₁-C₄-alkoxy, especially methoxy, ethoxy, n- and isopropoxy and also n-, iso- and tert-butoxy.

Halogen in the definitions of R¹, R² and R⁶ to R¹⁰ refers for example to fluorine, chlorine or bromine.

Preference is given to dyes of the formula (I) in which

-   R¹ is hydrogen, halogen, COOH or COOR¹¹, -   R² is hydrogen, halogen, COOR¹² or CN, -   R³ is C₁-C₄-alkyl or phenyl, -   R⁴ and R⁵ are each independently C₁-C₄-alkyl, -   R⁶, R⁷, R⁸, R⁹ and R¹⁰ are each independently hydrogen, halogen,     C₁-C₄-alkyl, C₁-C₄-alkoxy or COOR¹³, and -   R¹¹, R¹² and R¹³ are each independently C₁-C₄-alkyl.

Particular preference is given to dyes of the formula (I), in which

-   R¹ is hydrogen, fluorine, chlorine, COOH or COOR¹¹, -   R² is hydrogen, fluorine, chlorine, COOR¹² or CN, -   R³ is methyl, ethyl, n-propyl or isopropyl, -   R⁴ and R⁵ are each independently methyl, ethyl, n-propyl or     isopropyl, -   R⁶, R⁷, R⁸, R⁹ and R¹⁰ are each independently hydrogen, fluorine,     chlorine, methyl, ethyl, n-propyl, isopropyl, methoxy, ethoxy, or     COOR¹³, and -   R¹¹, R¹² and R¹³ are each independently methyl, ethyl, n-propyl or     isopropyl.

Very particular preference is given to dyes of the formula (I) in which

-   R¹ is COOCH₃, -   R² is hydrogen, -   R³ is methyl, -   R⁴ and R⁵ are methyl and -   R⁶, R⁷, R⁸, R⁹ and R¹⁰ are each independently hydrogen, methyl,     methoxy, ethoxy or chlorine.

Dyes of the formula (I) can exist as stereoisomers. The formula (I) particularly includes the following four E and Z isomers of the formulae (la) to (Id):

In which the substituents R1 to R10 have the general and preferred definitions specified for formula (I).

In an alternative embodiment, the present invention relates to methine dyes of the formula (Ia), in which the substituents R1 to R10 have the general and preferred definitions specified for formula (I).

Using the dyes of the formula (I) according to the invention, yellow to orange colouration of plastics, especially of polyamides, can be achieved, which are characterized by improved light fastness and improved thermal stability compared with the known yellow dyes used for these purposes. Moreover, the dyes according to the invention, surprisingly, also have improved colour strength compared to the known dyes.

It is possible using the dyes according to the invention to significantly outperform the property profiles achieved to date of known yellow dyes for plastic colouration. The present invention further relates to the use of the dyes of the formula (I) according to the invention for the bulk colouration of plastics. The dyes according to the invention can be used here individually or in any desired mixture with one another.

Bulk colouration in this case is understood to mean in particular methods in which the dye is incorporated into the molten plastic material, e.g. with the aid of an extruder, or in which the dye is already added to the starting components for preparing the plastic, e.g. to monomers prior to polymerization.

Particularly preferred plastics are thermoplastics, for example vinyl polymers, polyesters, polyamides and also polyolefins, especially polyethylene and polypropylene, polycarbonates and polyamide. Very particular preference is given to polyamides, especially nylon-6.6. and nylon-6.

In the context of the present invention, the term polyamides is used as a designation for synthetic, industrially usable thermoplastic plastics and thus differentiates this substance class from the chemically related proteins. Almost all significant polyamides are derived from primary amines, since the repeating unit consists of the —CO—NH— functional group. In addition, polyamides of secondary amines (—CO—NR—, R=organic radical) also exist. To prepare the polyamides, in particular aminocarboxylic acids, lactams and/or diamines and dicarboxylic acids serve as monomers.

Nylon-6.6 is usually prepared from hexamethylenediamine (HMD) and adipic acid. It is formed by a polycondensation with elimination of water.

Nylon-6 is obtainable by ring-opening polymerization of c-caprolactam with water as starter.

Suitable vinyl polymers are polystyrene, styrene-acrylonitrile copolymers, styrene-butadiene copolymers, styrene-butadiene-acrylonitrile terpolymers, polymethacrylate and polyvinyl chloride among others.

Suitable polyesters are, for example, polyethylene terephthalates, polycarbonates and cellulose esters.

The plastics to be coloured may be present individually or as mixtures with one another, as plastic materials or melts.

When used for the bulk colouration of plastics, the dyes (I) according to the invention are preferably applied in finely divided form for application, wherein dispersants may be, but do not have to be, used concomitantly.

When used for the bulk colouration of plastics, the dyes (I) according to the invention can be used for example directly in the process of the plastic preparation after the polymerization is complete. In this case, at least one dye (I) according to the invention is preferably mixed in dry form or ground with the plastic granules and this mixture is plasticized and homogenized for example on mixing rollers or in screws. However, the dyes (I) according to the invention may also be added to the molten liquid material and homogeneously distributed by stirring.

The material pre-coloured in this way may then be further processed as usual, e.g. by spinning to give bristles, threads etc. or by extrusion or in injection moulding processes to give mouldings.

Since the dyes (I) are resistant to polymerization catalysts, particularly peroxides, it is also possible to add the dyes (I) according to the invention to the monomeric starting materials for the plastic preparation, e.g. of polymethyl methacrylate (PMMA) and then to polymerize in the presence of polymerization catalysts. For this purpose, the dye is preferably dissolved in the monomeric components or mixed intimately with them.

The dyes of the formula (I) according to the invention for colouring the plastics mentioned, especially polyamide, are used preferably in amounts from 0.0001 to 1% by weight, especially 0.01 to 0.5% by weight, based on the amount of polymer.

By adding pigments insoluble in the polymers, for example titanium dioxide, it is possible to obtain corresponding useful covered colourations.

Titanium dioxide may be used in an amount from 0.01 to 10% by weight, preferably 0.1 to 5% by weight, based on the amount of polymer.

The present invention further relates to a method for the bulk colouration of plastics, wherein at least one dye of the formula (I) is mixed in dry form or is ground with at least one plastic, preferably in the form of granules, and this mixture is plasticized and homogenized, e.g. on mixing rollers or in screws.

However, the dyes (I) according to the invention may also be added to the molten liquid material and homogeneously distributed by stirring. It is likewise possible to add the dyes (I) according to the invention to the monomeric starting components in the plastic preparation and then to polymerize.

The material pre-coloured in this way may then be further processed as usual, e.g. by spinning to give bristles, threads etc. or by extrusion or in injection moulding processes to give mouldings.

By means of the method according to the invention, transparent or covered brilliant yellow colourations with very good heat and light resistance are obtained.

To carry out the method according to the invention, it is also possible to use mixtures of the dyes of the formula (I) according to the invention with other dyes and/or inorganic and/or organic pigments.

The present invention further relates to a method for preparing the dyes of the formula (I) according to the invention.

The dyes of the formula (I) according to the invention may be prepared by reacting at least one aldehyde of the formula (II)

in which

R¹, R², R³, R⁴ and R⁵ have the general and preferred definitions specified for formula (I),

with at least one acetanilide derivative of the formula (III)

in which

R⁶ to R¹⁶ have the general and preferred definitions specified for formula (I).

The aldehyde of the formula (II) can exist as stereoisomers. The formula (II) includes both possible E and Z forms.

The method for preparing the dyes (I) according to the invention by reacting the aldehydes of the formula (II) with the acetanilide derivatives of the formula (III) may be carried out in a manner known per se.

The method for preparing the dyes (I) according to the invention is carried out generally at a temperature in the range from −10 to 180° C., preferably from 0 to 100° C. and particularly preferably from 10 to 90° C.

The method for preparing the dyes (I) according to the invention is carried out generally at a pressure from 900 to 1100 hPa, preferably at standard pressure.

The method for preparing the dyes (I) according to the invention can be carried out in the presence of at least one solvent. Suitable solvents are those from the series of alcohols and formamides for example. The method for preparing the dyes (I) according to the invention is preferably carried out in the presence of at least one alcohol from the series of methanol, ethanol, propanol, and/or at least one formamide from the series of dimethylformamide and diethylformamide, particularly preferably in the presence of methanol and/or dimethylformamide.

The method for preparing the dyes (I) according to the invention is carried out in the presence of at least one base. Suitable bases are, for example, alkali metal hydroxides and alkali metal alkoxides. Preference is given to using lithium hydroxide, sodium hydroxide, potassium hydroxide and/or potassium tert-butoxide, particularly preferably sodium hydroxide and/or potassium tert-butoxide.

In general, the method for preparing the dyes (I) according to the invention is carried out such that the aldehyde (II) is firstly initially charged and the acetanilide derivative (III) is added and, after the reaction is complete, the compounds of the formula (I) are isolated. The isolation can be carried out by customary processes, preferably by filtration. The reaction product obtained can optionally be worked-up by further method steps such as washing and drying.

To carry out the method, generally 0.8 to 1.5 mol of acetanilide derivative (III) is used per mole of aldehyde (II). Preferably, 0.9 to 1.1 mol of acetanilide derivative (III) is used per mole of aldehyde (II) and particularly preferably 1 mol of acetanilide derivative (III) is used per mole of aldehyde (II).

Acetanilide derivatives of the formula (III) are known and can be purchased as commercial products from Alfa Acer for example.

The aldehydes of the formula (II) are also known and can be prepared, for example, in a two-stage synthesis in a manner known to those skilled in the art. Here, in a first stage a), at least one indole derivative of the formula (IV)

in which

R⁵ and R⁶ have the general and preferred definitions specified for formula (I), is reacted with at least one alkylating reagent and subsequently, in a second stage b), the intermediate of the first stage is reacted with at least one formylation reagent.

Reactions of the kind described in stage b) are known in the literature under the name of Vilsmeier reaction.

Generally, the reaction in stage a) is carried out such that the indole derivative of the general formula (IV) is initially charged and the alkylating agent is added optionally in the presence of a solvent.

The first stage a) of the reaction is carried out generally at a temperature in the range from 10 to 80° C., preferably from 20 to 70° C. and particularly preferably from 30 to 60° C.

The reaction in stage a) is carried out generally at a pressure from 900 to 1100 hPa, preferably at standard pressure.

The reaction in stage a) may be carried out in the presence of at least one solvent. Suitable solvents are those from the series of alcohols and water for example. The reaction in stage a) is preferably carried out in the presence of water as solvent.

In principle, all known alkylating reagents are suitable as alkylating reagent (see e.g. K. Schwetlick, Organikum, VEB Deutscher Verlag der Wissenschaften, Berlin, 15th Edition 1977, pages 260, 253, 674), such as dimethyl sulfate, methyl iodide or diazomethane. Preference is given to the use of dimethyl sulfate.

In general, at least one mole of alkylating reagent is used per mole of indole derivative. Depending on the structure of the indole derivative, corresponding to the above stoichiometry, even higher molar amounts may be used. Preferably, 0.9 to 1.1 mol, particularly preferably 1 mol of alkylating reagent is used per mole of indole derivative (IV).

The intermediate prepared in stage a) can be isolated by customary methods, by filtration for example. The intermediate prepared in stage a) is preferably further reacted directly without isolation in the subsequent stage b).

In general, the reaction in stage b) is carried out in such a manner that the alkylated compound from the first stage a) in the form of the reaction solution obtained is initially charged and the formylation reagent is added, optionally in the presence of at least one solvent, and subsequently the aldehyde of the formula (II) thus prepared is precipitated, optionally by the addition of a suitable amount of a suitable precipitant, and the aldehyde of the formula (II) is then isolated by customary methods, by filtration for example.

The reaction in stage b) is carried out generally at a temperature in the range from 10 to 80° C., preferably from 20 to 70° C. and particularly preferably from 30 to 60° C.

The reaction in stage b) is carried out generally at a pressure from 900 to 1100 hPa, preferably at standard pressure.

The reaction in stage b) may be carried out in the presence of at least one solvent. Suitable solvents are formamides for example. Preference is given to dimethylformamide and diethylformamide, particular preference being given to the use of dimethylformamide. When using dimethylformamide, it is particularly preferable to use this in excess wherein the dimethylformamide then serves as formylation reagent and solvent at the same time.

The formylation reagent used in stage b) is generally a mixture of at least one formamide and at least one phosphoric acid chloride.

Preferred formamides are dimethylformamide, diethylformamide and dibutylformamide.

A preferred phosphoric acid chloride is phosphorus oxychloride.

The formylation reagent used is particularly preferably a mixture of dimethylformamide and phosphorus oxychloride.

In general, at least one mole of formylation reagent, preferably 1.1 to 1.5 mol and particularly preferably 1.1 to 1 mol, is used per mole of alkylated compound from stage 1.

Suitable precipitants are, for example, alcohols such as methanol and/or ethanol.

The precipitant used is preferably methanol and/or ethanol, especially methanol.

The indole derivatives of the formula (IV) are known to those skilled in the art. They may be prepared in a manner known per se in a two-stage synthesis by reacting an aniline derivative of the formula (V)

in which

R¹ has the general and preferred definition specified for formula (I),

with a diazotization reagent and subsequent reaction with ring closure with a ketone of the formula (VI)

in which

R⁴ and R⁵ have the general and preferred definition specified for formula (I).

The diazotization reaction is generally carried out by initially charging the aniline derivative and adding the diazotization reagent at a temperature in the range from 0 to 10° C. at standard pressure in an aqueous medium.

In principle, any suitable diazotization reagent is an option as diazotization reagent. Preference is given to using an aqueous sodium nitrite solution.

In general, the diazotization reagent is used in an amount of at least two moles based on the aniline derivative (V).

The ring closure reaction with the ketone of the formula (VI) is carried out in a manner known per se in a one-pot reaction by reducing the diazonium salt of the aniline derivative (V) to the hydrazone and by reacting the hydrazone with the ketone of the general formula (VI), preferably at a temperature in the range from 40 to 100° C., preferably in aqueous solution, and subsequently by isolating and washing the indole derivative of the formula (IV) by customary methods, preferably filtration.

The aniline derivatives of the formula (V) and the ketones of the formula (VI) are known and can be purchased as commercial products, from Alfa Acer or Sigma-Aldrich for example.

The invention is elucidated but not limited by the following examples, in which the parts are by weight and percentage values are percent by weight (% by weight).

EXAMPLES Example 1

Preparation of the Inventive Compound of the Formula (I)

where R¹=COOCH₃; R²=H; R³, R⁴ and R⁵=CH₃ and R⁶, R⁷ R⁸ and R⁹=H and R¹⁰=OCH₃

Into a mixture of 160 ml of acetic acid and 12 ml of acetic anhydride were introduced 25.9 g (=0.1 mol) of aldehyde of the formula (II) where R¹=COOCH₃; R²=H; R³, R⁴ and R⁵=CH₃ and also 20.7 g (=0.1 mol) of acetanilide derivative of the formula (III) where R⁶, R⁷ R⁸ and R⁹=H and R¹⁰=OCH₃ and also 5 g of ammonium chloride. The mixture was subsequently heated to a temperature of 102° C. and stirred for 6 hours. The mixture was then cooled to 25° C. and 140 ml of methanol were added. The reaction product was isolated on a Nutsche filter. The filter cake was washed with ca. 600 ml of methanol and ca. 2000 ml of water at a temperature of 90° C. The washed product was dried in a vacuum drying cabinet at a temperature of 80° C. and a pressure of 200 hPa.

Yield: 36.3 g (corresponds to 81% of theory), melting point 230° C.

Examples 2 to 8

Preparation of inventive compounds of the formula (I) in which the substituents R¹ to R¹⁰ have the definitions listed in Table 1.

TABLE 1 Example R¹ R² R³ R⁴ R⁵ R⁶ R⁷ R⁸ R⁹ R¹⁰ 2 COOCH₃ H CH₃ CH₃ CH₃ OCH₃ H Cl OCH₃ H 3 COOCH₃ H CH₃ CH₃ CH₃ CH₃ H Cl H H 4 COOCH₃ H CH₃ CH₃ CH₃ CH₃ H CH₃ H H 5 COOCH₃ H CH₃ CH₃ CH₃ Cl H H H H 6 COOCH₃ H CH₃ CH₃ CH₃ CH₃ H H H H 7 COOCH₃ H CH₃ CH₃ CH₃ H H OCH₃ H H 8 COOCH₃ H CH₃ CH₃ CH₃ H H OC₂H₅ H H

The preparation and work-up of the compounds of examples 2 to 8 were each carried out in analogy to example 1 but with the following deviations:

Example 2

Instead of the acetanilide derivative used in example 1, 27.2 g (=0.10 mol) of acetanilide derivative of the formula (III) were used where R⁶ and R⁹=OCH₃; R⁷ and R¹⁰=H and R⁸=Cl.

Yield: 43.6 g (corresponds to 85% of theory), melting point 248° C.

Example 3

Instead of the acetanilide derivative used in example 1, 22.6 g (=0.10 mol) of acetanilide derivative of the formula (III) were used where R⁶=CH₃; R⁸=Cl and R⁷, R⁹ and R¹⁰=H.

Yield: 41.1 g (corresponds to 88% of theory), melting point 238° C.

Example 4

Instead of the acetanilide derivative used in example 1, 20.5 g (=0.10 mol) of acetanilide derivative of the formula (III) were used where R⁶ and R⁸=CH₃ and R⁷, R⁹ and R¹⁰=H.

Yield: 28.6 g (corresponds to 64% of theory), melting point 213° C.

Example 5

Instead of the acetanilide derivative used in example 1, 21.2 g (=0.10 mol) of acetanilide derivative of the formula (III) were used where R⁶=Cl and R⁷, R⁸, R⁹ and R¹⁰=H.

Yield: 38.9 g (corresponds to 86% of theory), melting point 209° C.

Example 6

Instead of the acetanilide derivative used in example 1, 19.1 g (=0.10 mol) of acetanilide derivative of the formula (III) were used where R⁶=CH₃ and R⁷, R⁸, R⁹ and R¹⁰=H.

Yield: 28.5 g (corresponds to 66% of theory), melting point 179° C.

Example 7

Instead of the acetanilide derivative used in example 1, 20.7 g (=0.10 mol) of acetanilide derivative of the formula (III) were used where R⁸=OCH₃ and R⁶, R⁷, R⁹ and R¹⁰=H.

Yield: 31.8 g (corresponds to 71% of theory), melting point 202° C.

Example 8

Instead of the acetanilide derivative used in example 1, 22.1 g (=0.10 mol) of acetanilide derivative of the formula (III) were used where R⁸=OC₂H₅ and R⁶, R⁷, R⁹ and R¹⁰=H.

Yield: 31.5 g (corresponds to 68% of theory), melting point 211° C.

Preparation of the Precursors Example 9

Preparation of an Aldehyde of the Formula (II)

where R¹=COOCH₃; R²=H and R³, R⁴ and R⁵=CH₃

a) Diazotization:

139.9 g of p-aminobenzoic acid were introduced to 270 g of 30% hydrochloric acid and the mixture was cooled to 0° C. by externally cooling. Subsequently, 174 g of a 40% aqueous solution of sodium nitrite were added. The mixture was stirred for 30 minutes and then the excess nitrite was removed with ca. 0.5 g of amidosulfonic acid.

b) Preparation of the Hydrazone and Ring Closure:

A mixture of 250 g of water and 660 g of sodium hydrogen sulfite, in the form of a 39% aqueous solution, was adjusted to a pH of 6.5 with 80 g of a 40% aqueous sodium hydroxide solution. Over the course of ca. 30 minutes, the diazotization solution prepared in stage a) was added, while maintaining a pH of ca. 6.5 by addition of 100 g of a 40% aqueous sodium hydroxide solution. Subsequently, the reaction mixture was stirred at a temperature of 40° C. for ca. 1 hour. Subsequently, 560 g of 96% sulfuric acid and then 86.1 g of methyl isopropyl ketone were added dropwise. The reaction mixture was heated to 70° C. and stirred for ca. 4 hours. The reaction mixture was subsequently heated to 80° C. and then stirred again for ca. 4 hours. The reaction mixture was then cooled to 25° C. and the pH was adjusted to 6.5 with ca. 800 g of a 40% aqueous sodium hydroxide solution. The reaction mixture was stirred for 30 minutes and the reaction product was then isolated on a Nutsche filter and washed with 2 litres of water.

c) Preparation of the Aldehyde:

The moist press cake of the ring-closed product from stage b) was introduced into 1200 g of water. The pH was then adjusted to 10 with ca. 70 g of a 40% aqueous sodium hydroxide solution. Over the course of 1 hour, 325 g of dimethyl sulfate were added dropwise maintaining a pH here of ca. 8.5 by addition of 200 g of a 40% aqueous sodium hydroxide solution. The reaction mixture was heated to 40° C. and stirred for ca. 5 hours. The reaction mixture was subsequently heated to 60° C. and then stirred for a further 1 hour. The reaction mixture was then left to stand whereupon a phase separation took place within 1 hour. The aqueous phase was then removed. Residual water was removed from the organic phase under reduced pressure at 80° C. and 20 mbar. 310 g of dimethylformamide were then added dropwise to the organic phase. Subsequently, 263 g of phosphorus oxychloride were added at 40° C. over the course of 3 hours and the reaction mixture was stirred for 5 hours. The mixture was then cooled to 20° C. and 160 g of methanol were added. The pH was then adjusted to 11 with ca. 200 g of a 40% aqueous sodium hydroxide solution. The reaction mixture was subsequently stirred for 60 minutes and then the reaction product was isolated on a Nutsche filter and washed with 160 g of methanol and 2000 g of water. The washed product was dried in a vacuum drying cabinet at a temperature of 80° C. and a pressure of 200 mbar.

Yield: 176.3 g (corresponds to 68% of theory)

List of Substances Purchased:

Molecular Name: weight Cas. No. Content Manufacturer p-Aminobenzoic acid 137.2 150-13-0 98 Sigma-Aldrich Methyl isopropyl ketone 86.1 563-80-4 99 Sigma-Aldrich 2-Acetoacetanilide 207.2 92-15-9 99 Sigma-Aldrich 4-Chloro-2,5- 271.7 4433-79-3 98 ABCR-Chemie dimethoxyacetoacetanilide 4-Chloro-2- 225.7 20139-55-3 98 ABCR-Chemie dimethylacetoacetanilide 2,4-Dimethylacetoacetanilide 205.3 97-36-9 99 ABCR-Chemie 2-Chloroacetoacetanilide 211.7 93-70-9 98 Sigma-Aldrich 2-Methylacetoacetanilide 191.2 93-68-5 98 Sigma-Aldrich 4-Acetoacetanilide 207.2 5437-98-9 98 ABCR-Chemie

The results of the UV/VIS measurements and absorption values for the inventive compounds of examples 1 to 8 are listed in table 2.

TABLE 2 Inventive Absorption maximum compound UV/VIS spectrum¹⁾ E 1/1 value²⁾ Example 1 449 nm 1650 Example 2 453 nm 1470 Example 3 453 nm 1800 Example 4 449 nm 1620 Example 5 450 nm 1830 Example 6 450 nm 1760 Example 7 448 nm 1450 Example 8 447 nm 1440 ¹⁾The UV/VIS absorption spectra of the inventive compounds were all measured in the solvent 1-methoxy-2-propyl acetate (CAS No. 108-65-6). ²⁾The E1/1 value specified is a hypothetical absorption value. Initially measured is the absorbance of a solution of the respective sample in 1-methoxy-2-propyl acetate in a cuvette of 1 cm path length, wherein the concentration of the solution is selected such that the absorption value observed at the absorption maximum is about 1. The value determined is then converted to a concentration of 1 percent by weight whereby the E1/1 value is obtained.

Practical Results:

A) Description of the “Thermal Stability” Test Method

In a tumbling mixer, 2 g each of the dye to be tested were mixed with 1998 g of a PA6 granulate of the Durethan B30S type (commercial product from Lanxess Deutschland GmbH) with 1% TiO₂ which had been dried at 80° C. for 4 hours. This mixture was extruded at a material temperature of at most 240° C. in a single-screw extruder (Stork, 25 mm screw), cooled with water, granulated using a granulator from Sheer and dried at 80° C. for 8 hours. The heat stability of the resulting plastic granules was tested according to DIN EN 12877-2 (“Determination of colour stability to heat during processing of colouring materials in plastics”) (method A) on an injection moulding machine. A sample as standard was prepared at 240° C. with a residence time in the screw of 2.5 minutes. Compared to this standard sample, the samples to be determined were evaluated coloristically, which were prepared at a residence time of 5 minutes and temperatures of 240-320° C. Samples with an overall colour difference (calculated in accordance with EN ISO 11664-4) of dE 3.0 were evaluated as stable at the applied temperature.

The results of the thermal stability determination of the inventive compounds of examples 1 to 8 and also the non-inventive comparative compounds of the prior art are listed in tables 3 and 4.

TABLE 3 Inventive compound Heat stable to (° C.) Example 1 335 Example 2 340 Example 3 335 Example 4 345 Example 5 335 Example 6 340 Example 7 335 Example 8 345

TABLE 4 Non-inventive compound Heat stable to (° C.) D.Y 201 (Macrolex Yellow 6G) Decolourization at 240° C. S.Y. 93 (Macrolex Yellow 3G) Decolourization at 240° C. S.Y 114 (Macrolex Yellow G) 240° C. S.Y 160:1 (Macrolex Fluor. <240° C. (DE 3.6 at Yellow 10GN) 240° C.) Example 8 of EP-A 3 048 138 320° C. Example 9 of EP-A 3 048 138 320° C. 

What is claimed is:
 1. A dye of the formula (I)

in which R¹ is hydrogen, halogen, COOH or COOR¹¹, R² is hydrogen, halogen, COOH, COOR¹² or CN, R³ is alkyl or phenyl, R⁴ and R⁵ are each independently alkyl, R⁶, R⁷, R⁸, R⁹ and R¹⁰ are each independently hydrogen, halogen, alkyl, alkoxy or COOR¹³, and R¹¹, R¹² and R¹³ are each independently alkyl.
 2. The dye of claim 1, wherein in formula (I) R¹ is hydrogen, halogen, COOH or COOR¹¹, R² is hydrogen, halogen, COOR¹² or CN, R³ is C₁-C₄-alkyl or phenyl, R⁴ and R⁵ are each independently C₁-C₄-alkyl, R⁶, R⁷, R⁸, R⁹ and R¹⁰ are each independently hydrogen, halogen, C₁-C₄-alkyl, C₁-C₄-alkoxy or COOR¹³, and R¹¹, R¹² and R¹³ are each independently C₁-C₄-alkyl.
 3. The dye of claim 1, wherein in formula (I) R¹ s hydrogen, fluorine, chlorine, COOH or COOR¹¹, R² is hydrogen, fluorine, chlorine, COOR¹² or CN, R³ is methyl, ethyl, n-propyl or isopropyl, R⁴ and R⁵ are each independently methyl, ethyl, n-propyl or isopropyl, R⁶, R⁷, R⁸, R⁹ and R¹⁰ are each independently hydrogen, fluorine, chlorine, methyl, ethyl, n-propyl, isopropyl, methoxy, ethoxy, or COOR¹³, and R¹¹, R¹² and R¹³ are each independently methyl, ethyl, n-propyl or isopropyl.
 4. The dye of claim 1, wherein in formula (I) R¹ is COOCH₃, R² is hydrogen, R³ is methyl, R⁴ and R⁵ are methyl, and R⁶, R⁷, R⁸, R⁹ and R¹⁰ are each independently hydrogen, methyl, methoxy, ethoxy or chlorine.
 5. A method for the bulk colouration of plastic, the method comprising adding one or more dyes of claim 1 into plastic as colorants for the plastic.
 6. The method of claim 5, wherein the plastic is one or more plastics selected from the group consisting of vinyl polymers, polyesters, polyolefins, polycarbonates, and polyamides.
 7. The method of claim 5, wherein the plastics are nylon-6 and/or nylon-6.6.
 8. The method of claim 5, wherein the method comprises adding to the plastic, an amount of 0.0001 to 1 percent by weight of the dyes, based on the amount of plastic.
 9. The method of claim 5, wherein the method comprises adding to the plastic, an amount of 0.01 to 0.5 percent by weight of the dyes, based on the amount of plastic.
 10. A method for the bulk colouration of plastic, the method comprising mixing the one or more dyes of claim 1 in dry form with one or more plastics, or, grinding the one or more dyes in dry form with one or more plastics, to produce a mixture, and melting and homogenizing the mixture.
 11. The method of claim 10, wherein the one or more plastics are in the form of granules.
 12. A method for the bulk colouration of plastics, the method comprising adding the one or more dyes of claim 1 to a molten plastic material comprising one or more plastics to form a mixture, and then homogenizing the mixture.
 13. A method for the bulk colouration of plastics, the method comprising mixing the one or more dyes of claim 1 with monomeric starting components for producing one or more plastics, and subsequently polymerizing the monomeric components.
 14. A method for the bulk colouration of polymethyl methacrylate (PMMA), the method comprising mixing the one or more dyes of claim 1 with one or more methyl methacrylate monomers to form a mixture, or dissolving the one or more dyes therein to form a solution, and polymerizing the monomers in the mixture or solution in the presence of one or more polymerization catalysts.
 15. A plastic composition comprising the one or more dyes of claim
 1. 16. The plastic composition of claim 15, wherein the plastic composition is a polyamide composition or a polymethyl methacrylate.
 17. A moulding comprising one or more plastic compositions of claim
 15. 18. A method for producing a dye of claim 1, the method comprising contacting one or more aldehydes of the formula (II)

in R¹, R², R³, R⁴ and R⁵ have the definitions specified in claim 1, with one or more acetanilide derivatives of the formula (III)

in which R⁶ to R¹⁰ have the definitions specified in claim
 1. 